Administration of vitamin A to pregnant mice on day 10 of gestation inhibits cartilage formation in the developing face and limbs. The purpose of this project is to determine the molecular basis of this inhibition of cartilage development. Mesenchyme cells from prechondrogenic day 10 mouse limb buds are dissociated with trypsin and plated out at high cell density. Control cultures differentiate into cartilage but vitamin A treated cultures remain mesenchymal. The developmental changes taking place in control and vitamin A treated cultures are being monitored in terms of fine structure, proteoglycan synthesis, glycopeptide synthesis and collagen synthesis. A culture system which allows in vitro secondary palatal shelf elevation and remodeling in mice is also under development. Time-lapse filming of the elevation event will document the presence or absence of a peristaltic wave moving from the posterior toward the anterior of the shelf. Drugs will be administered in an attempt to stimulate precocious elevation or to block it and, thereby, directly test the importance of various cellular activities in elevation.